Calpal,
I see your point about trying to be organised in advance but there's not much you can do at this stage! People on NATS 219 (due to start April/May) are still in the process of getting to know each other and sort out accommodation - there's plenty of it in Bournemouth to go around so no worries there and everything does seem to get sorted out rather last minute....
Rightmove.co.uk has a load of stuff on there if you're curious, as does gumtree and check out facebook groups for NATS 218 or NATS 219 for discussions on B&B's.